Oil-filled electrical instrument

ABSTRACT

An oil-filled electrical instrument is manufactured by connecting a coil-core assembly with a hollow member, forming a porous layer around the coil and hollow member, covering the porous layer with a substantially impervious layer of an uncured plastic material, curing the plastic material, and then introducing an insulation oil into the hollow member to impregnate the coil with the oil. The plastic layer minimizes the amount of insulation oil necessary to prevent corona discharge to thereby decrease the weight of the electrical instrument and minimize the possibility of accidental fire of the instrument.

United States Patent 11 1 1111 3,905,001 Sato et a1. Sept. 9, 1975 [54] OIL-FILLED ELECTRICAL INSTRUMENT 3,138,773 6/1964 Nichols et al 336/94 X 3,233,311 2/1966 6' e ich et a1. 336/94 X [751 Inventors: KohelsfltlKawamshl? Yshlakl 3,587,168 6/1971 K iitc ir 336/94 X Hal/ash, Takaraluka, both Of Japan 3,766,505 10/1973 Sato 336 94 [73] Assignee: Matsushita Electric Industrial Co., FOREIGN PATENTS OR APPLICATIONS Kadoma, Japa 660,056 3/19 3 Canada 336/96 22 F1166; 061. 24, 1973 Primary ExaminerThomas J. Kozma [21,] Appl" 409,064 Attorney, Agent, or Firm-Stevens, Davis, Miller &

Mosher [30] Foreign Application Priority Data Oct. 31, 1972 Japan 47-109682 [57] ABSTRACT Oct 31, 1972 Japan 47409683 An oil-filled electrical instrument is manufactured by connecting a coil-core assembly with a hollow mem- 52 US. Cl. 336/94; 174/17 LF; 174/52 PE; her, forming a porous layer around the coil and hollow 3 9 member, covering the porous layer with a substantially 51 1m. (:1. H0lf 27/02 impervious layer of an uncured Plastic material, curing [58], Field of Search 336/94, 9 58, the plastic material, and then introducing an insulation 174/17 R, 17 LP, 52 PE oil into the hollow member to impregnate the coil with the oil. The plastic layer minimizes the amount of in- [56] References Cited sulation oil necessary to prevent corona discharge to V UNITED STATES PATENTS thereby decrease the weight of the electrical instru- 2 I41 14] 12/1938 K t d 336/94 ment and minimize the possibility of accidental fire of ongs e 2,168,154 8/1939 Camilli 336/94 the Instrument I 2,297,605 9/1942 Camilli 336/94 6 Claims, 2 Drawing Figures PATENTH! SEP 1975 FIG.

FIG.2

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Y 1 OIL-FILLED ELECTRICAL INSTRUMENT FIEID OF THE INVENTION '1 I The present invention relates to an oil-filled electrical instrument, i.e., an electrical device disposed in a quantity of insulation oil, such as an oil-filled transformer, reactor or capacitor, and to a method of manu-' instrument is filled with such a large amount of insulation oil (usually mine'ral oil of a lower ignition point) that it is liable to produce a large fire when the oil is ignited by'anaccidental trouble such as a shortcircuit.

The electrical elements and insulation oil are conveniently receivedin a closed container, the container preventing deterioration" of the'o'il after a prolonged op-' erative time of theelectrical instrument. The closed container needs an arrangement toabsorb the variation the volume of the insulationl'oil caused either by the variation in the atmospheric temperature at which the electrical instrument is operate rigor by temperature rise'.' Such an arrangement will be termedv a breathing ech nini hereunder. Lack of .a breathing mecha-. nism will a partial vaecum within a closed container when insulation oil contracts, which in turn pro duces in the insulation oil voids about which corona discharges are produced to cause dielectric breakdwn, Oriithe otherhand, if insulation oil is expanded, pressure will build up in the oil to deform the closed container untilit is destroyed."

' The larger the amount of insulation oil in a closed container, the greater is the required breathing mechanism. In an attempt to reduce the amount of insulation oil necessary to fill up the space a closed container, has been proposedto dispose a spacer element in the container The pro sal, howeven has failed to provide thedesir e df result. Y v v v bry insulation is useful toproduce small-sized and light-weight electrical ins t rumcnts but fails to avoid formationof voids in the instruments on electrical componentssu chias' conductors. The voids allow production of corona discharge which dielectric breakdown; Thus dryinsulationzis not employed in electrical instruments c tcepting those used with low voltages in order to assure prolonged operative lives of the instruments j g M ARY OF Tl-lElNVENTlONJ The present invention aimslo providefnovcl and improved structures of oil-filled electrieal instruments which eliminate corona discharge and a method of manufacturing the improved electrical" instruments.

I According toa feature of the present invention, there is provided an oil-filled electrical instrument, comprising an innerparna layer of porous'inaterial surrounding said inner part, a substantially imprevious layer er a plastic matcrialjaroundsaid porous layen sa id inner partand said porous layer being impregnated with an insulation oil, and a passage extending outwardly from said inner part through said layers to provide a pouring port for the insulation oil.

According to another feature of the present invention, there is provided an oil-filled electrical instrument, comprising an inner part surrounded by a layer of a plastic material of a characteristic that the rate of variation of the viscosity of the plastic rnaterial with'respect to the lapseof time when the plastic material is cured is zero or of a positive value, said inner being impregnated with an insulationoihand a passage ex tending outwardly from said inner part throughsaid plastic layer to provide a pouring port for the insulation Oil. I I i I I According to a further feature of the present inven-' tion', there is provided a method of manufacturing an oil-filled electrical instrument having an inner part, said method comprising the steps of connecting said inner part with a hollow member, forming a porous layer around at least a partof said inner part and at least a part of said hollow member, covering said porous layer with a substantially impervious layer of an uncured plastic material, curing said plastic material, and introducingan insulation oil into said hollow member to im pregnate said inner part with the oil. 7 I f According to a still further feature of the present in: vention, there is provided a method of manufacturing an oil-filled electrical instrument having an inner part, said method comprising the steps of connecting said inner part with a hollow member, covering at least a part of said inner part and at leasta part of said hollow member witha layer of uncured plastic material having a characteristic that the rate of variation of the viscosity of the plastic material with respect to the lapse of time when theplastic material iscured is zero or 'of a positive value, curing said plastic material, and introducingan' insulation oil into said hollow member to irnpregnate said inner part. with said oil. I g, v

The present invention will be described by way of e gample with reference to the accompanying drawings".

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a partial sectional side elevation of a trans- DESCRIPTION- OF PREFERRED EMBODIMENTS r transformer shown in E16. 1 includes primary and secondary coils generally'indicat'ed by 3. An oil passage provided by a hollow member 4 interconnects a part of the coils 3 and the. outside of the transformer.

The coils and a part of the oil passage are surrounded by a layer 8 of an insulating porousmaterial which may comprise a composite material formed therein with quite finc or small perforations communicated with each'other to provide an oil permeable property.

The porouslayer S rnay be formed by thcffollow'ing process. A plastic material such as soluble phenolic or epoxy resinand'a powderyinorganic material such as powdered calcium carbonate are mixed in a solvent to form a solution of the mixture. Coils 3 before assemblec'l with other elements into a transformer arc dipped into the solution and removed therefrom to allow the solvent on the coils to volatilize. Thereafter, the coils are'heated to an elevated't 'enipera'ture to cure the plastic material contained in the mixture so thatthccoils are'covered'with'a perforated layer.

Thereafter, the coils are assembled with a core 2 The assemblyis then placed in a casing l. The'eoils 3 are then connected with lead'wires 5, l and l1, respectivelyfwhieh turn areconneeted to terminals 6, 13 and "14, respectively. Thereafter, a liquid lplastic'rnaterialwhic h'forms a dense or substantially impervious I laye'rfis poured intothe' easing 1 so as not to be in duced into the oil. passage use that-the space in the cas irig its filledwith the plastic material 9. n1 err'riirial coV'er s'thetop or-me oilp' assage wand-is providedwith an opening7 through which insulation oil 15 is poured into the oil passage 4 and thus into the coils 3 so that the coils are impregnated with the oil. vacuiim may be app'lie'd'to the coils to facilitate theimpr'egn ation. The 6pe'ning'7"istheri sealed or closed byme'ans" of Sewering to secur'cthe lead wire tdthtrmirial' 6. Refer ence'rr'u ner'al l2 denotes solder by which the lead wire is'secured to "the terminal 13.

Theinsulation" o'il thus pour'edinto the transformer fills up the spaces not only in the coils 3 and the perforatd'p'lastic layer butalso any space which would be defined between the plastic layer 9' and the porous layer 8 to avoid corona discharge Contrary to theinvention, if theeoils 3 are not'conn'ctedwith the hollow 'mernber 43nd thus have tb be a s's'embled into a trahsfor'mer'after impregnation with I i nsulation oilfthe insulation oil will flow out of the dciils during? assembly to produce non-impregnated parts iii the eoils 'with a resultant possibility of corona diseharge'. lrraddition, the insulation 'oilfmay tiisa d'v an geou'sly be'mixed with filling plastfc material with resultant'iincorn'pl'e'te curing dfthe' plastic material and thus po'or adhesion between the latter and the leadwir e s and terminals; 5 Y "'The' embodiment shown inFlG. 1 is equipped with the casing 1, Thecasing; however, is not essentially necessary' and' the layer of the filling plastic material 9 mayiorrn the outer su'rfa ce' of the transformer.

In place of the mixture which. forms .the porous layer 8, another plastic material may be used which has such a characteristic that when 'it is curedi the viscosity of I:

however, uses a plastic material such as silicone rubber having a characteristic that the viscosity of the material is ri'ot'lowered during the curing of the material. Thus,

' t u" .1 z f thepl'astie material is not once decreased but gradually increased, i.e., a characteristic that when the'plastie material becomes solidified, the rate of vari ation in the viscosity of the plastic material with respect'to"the'laps'e of time is always zero or of a positive value. As a further M ing an opening? in the "top surface thereof. insulation" oil 15 is poured through the opening7- and flows'into' resin by virtue of capillaryeffect. lf the coilsare re moved from the uncured're'sin',fthe coating on the coils willforrn adense layer whcn'the coatingis cured. lfa plastic material 'is' usedwhich has a hysteresis characteristic that the viscosity ofthe'plastic'material when curedis'onc'e lowered (for example, the' viscosity of a certain plastic materialsuch -asthe usually epoxy resin when curedis once decreasedtof'l/ 110 and then increased. the'plastic materialwill penetrate into the coils 3 due to the lowered viscosity of'the' material even if the plastic material was initially adjusted'with respect toits viscosity; with a resultant disad'varitage' plastic material does not' pe'netrate into the coils when coveringlayers are formed 'therearound.

Preferably, the filling plastic material 9 is the same as the plastic material of. the layer 8. This feature is advantageous in that the filling material 9 is completely adhered' to theflayerfi to avoid any gapwhich would otherwise giveriseto the production of corona discharge. Referring to FIG; 2 a' second embodiment of the iriventi'on will be described hereunder. The" embodiment comprises a fly-backhransfo'rr'ner which is a kind' of transformer disposed in the horiz'ontal fdefleetion' circuit of a television image receiver to produce a high voltage jby mean's of fly-back pulses: fly-back transformer known to have'deficiencies such as increased loss and variation inits high voltag'e'output due to large variations in its operation characteristics. The varia-' to el irniiiate thevariation orin'cr ease ih the st i-ay capac itancel' Hovvever i'theproposed plastic"casing is not cornpletely'satisfafetory b'CatlSe the 'ca'sing i's riot' flexiblean'd terids to bedestroyed bythe pressure of the oil withinthee'asin g. s I

According to the present inventionl'a fly-back transformer is enabled to be equipped with anoute'r' ca si'ng of a plasticmaterialiarid to havea 1st'ableoperating characteristic which is not 'changedby"the variatiori inthe oil pressure. The fly-back transformer sho'wn'in' FlG.'2 can be manufactured by a rnethodsim'ilar to the method described with reference to F-IG. -hand has an outer casing 1' of a plastic material. Coils '3 are dis posed in the casing and have apart in c ommunication with an oil passage 4' formedof a plasti'cmaterialfThe coils Sand the oil passage4 a re's'urrounde 'd by a layer 8 similar to the layer Sin FIG. 1 The coils 3 areasseinbled witha' core 2"of fer-rite to form an'as'sernbly. The space'betw'een'the assembly and the outer casing 1 is filledwith a plasticmaterial9."Terrniiials 14'fa're con-' n'ectcd to s me 0f the windings ofthe coils 3. Rectifiers 1 6'aredisposed withih the oil passage 4. The top of the passage 4 is c'ov'er'efdwitha bellows 17 of a metal havthe oil passage and thus into the coils 3 along paths indicated hydotted arrows "18]. The opening 7 in the bellows 17 is closed after the pouring so that the bel-' lows acts'both ,as'a' 'terniinaland as a breathing mechanism A protector :19 fora terminal for high voltage outputis mountedon thcjtop surface ofthe plastic material I a The abovedescribed'and*illustrated embodiments of the invention provide thefollowing advantages:

l'.-'l3 ei;ausc an in sulating; layerof oil-*for preventing corona discharge isflforrned only in the. coils and around the part through which high voltage is applied, a minimum amount of insulation oil is required with resultant decrease in the weight of the products and in the possibility of accidental fire.

2. As the coils are impregnated with oil by means of vaccum impregnation after the space between the coils and the outer casing is filled with a plastic material, the impregnation is complete and does not produce any void in transformer which would otherwise cause corona discharge.

What we claim is:

1. A fly-back transformer, comprising a coil; a layer of porous material surrounding substantially all of the surfaces of said coil, said coil and said porous layer being impregnated with an insulation oil; a core assembled with said coil into a coil-core assembly; a casing of an electrically insulating material housing said coilcore assembly; a passage extending outwardly from said coil to the outside of said casing to provide a pouring port for the insulation oil; and a substantially impervious layer of a plastic material filling up the space defined between said core, said coil, said passage and said casing.

2. A fly-back transformer comprising a coil impregnated with an insulation oil. substantially all of the surfaces of said coil being covered with a layer of a plastic material of a characteristic such that the rate of variation of the viscosity of the plastic material with respect to the lapse of time when the plastic material is cured is one of zero and positive values; a core assembled with said coil to form a coil-core assembly; a casing of an electrically insulating material housing said coilcore assembly; a passage extending outwardly from said coil to the outside of said casing to provide a pouring port for the insulation oil; and a substantially imper' vious layer of a plastic material filling up the space defined betwecn said core, said coil, said passage and said casing.

3. A fly-back transformer as claimed in claim 1 which further comprises means covering the opening of said insulation oil pouring port for enabling breathing of said transformer.

4. A fly-back transformer according to claim 3 in which said breathing enabling means comprises a bellows member. I

5. A fly-back transformer as claimed in claim 2 which further comprises means covering the opening of said insulation oil pouring port for enabling breathing of said transformer.

6. A fly-back transformer as claimed in claim 5 in which said breathing means comprises a bellows member. 

1. A fly-back transformer, comprising a coil; a layer of porous material surrounding substantially all of the surfaces of said coil, said coil and said porous layer being impregnated with an insulation oil; a core assembled with said coIl into a coil-core assembly; a casing of an electrically insulating material housing said coil-core assembly; a passage extending outwardly from said coil to the outside of said casing to provide a pouring port for the insulation oil; and a substantially impervious layer of a plastic material filling up the space defined between said core, said coil, said passage and said casing.
 2. A fly-back transformer comprising a coil impregnated with an insulation oil, substantially all of the surfaces of said coil being covered with a layer of a plastic material of a characteristic such that the rate of variation of the viscosity of the plastic material with respect to the lapse of time when the plastic material is cured is one of zero and positive values; a core assembled with said coil to form a coil-core assembly; a casing of an electrically insulating material housing said coil-core assembly; a passage extending outwardly from said coil to the outside of said casing to provide a pouring port for the insulation oil; and a substantially impervious layer of a plastic material filling up the space defined between said core, said coil, said passage and said casing.
 3. A fly-back transformer as claimed in claim 1 which further comprises means covering the opening of said insulation oil pouring port for enabling breathing of said transformer.
 4. A fly-back transformer according to claim 3 in which said breathing enabling means comprises a bellows member.
 5. A fly-back transformer as claimed in claim 2 which further comprises means covering the opening of said insulation oil pouring port for enabling breathing of said transformer.
 6. A fly-back transformer as claimed in claim 5 in which said breathing means comprises a bellows member. 